Using `Value.as_unit` raises an import error if Pint is not installed (and Pint is not a requirement)

[alexhroom]

Currently, if a user tries to perform unit conversion on a Value object and does not have pint installed, it raises an error:

from orsopy.fileio.model_language import Value

val = Value(5.0, 'nm')
val.as_unit("angstrom")

produces an import error for pint. This is a problem because pint is not an installation requirement for orsopy, but it seems orsopy depends on it. I think that either:

• pint needs to be added to the requirements (and then the pint types can be used instead of the orsopy Value classes!)
• or
• a more descriptive error telling the user that they can only do unit conversions if they install pint should be added (and maybe popular unit conversions like nm <-> angstrom can be provided by orsopy itself)

[aglavic]

Hi @alexhroom ,

yes, you are right. The design idea here was, that this is a purely convenience method and thus pint was not added to the orsopy requirements.
I agree, we should catch that expected error and re-raise with a more descriptive one.

We can't just replace Value with pint alternatives, as it is a class mirroring orso header standards that have other optional parameters.